This invention relates to a transparent protective laser shield and the method of making the same which is adapted to be interposed between a laser and a viewer for protecting the viewer from damage by laser beam radiation, and more particularly to such protective laser shield in which an interference filter is bonded directly onto a ballistic protective substrate which may incorporate absorption dyes thereby providing a protective laser shield having ballistic protection properties as well as laser radiation rejection properties.
There has been a proliferation of laser use in medical, industrial, space and military applications in which a laser beam is employed for cutting, fusing, or performing other functions which may cause contact with the eye either by direct viewing or reflection from the objects to which the laser beam is applied. The eye collects and focuses the energy, and since the laser beam is generally concentrated, considerable damage can result from the application of this energy to the optic nerve. The same is true when that viewer happens to be a light sensitive detector which may be monitoring or viewing the particular operation or system in which the laser beam is operating. Accordingly, laser shields have been provided to enable viewing the laser beam in its environment without being subjected to the danger of concentrated laser beam energy.
U.S. Pat. No. 3,853,783 describes the use of vanadyl phthalocyanine sulfonides in plastic compositions to protect the eyes from exposure to laser radiation in the region of about 620 to 720 nm. U.S. Pat. No. 4,657,345 which is assigned to the assignee of the present invention, a laser shield is provided by diffusing a particular absorption dye into a transparent plastic substrate which absorbs radiation of interest. In U.S. Pat. No. 4,622,174 which is assigned to the assignee of the present invention absorption dyes are provided in an optical laser shield which absorb narrow band wavelengths which can be adjusted to coincide with the selective wavelengths of the laser beams which are desired to be protected against.
Interference filters comprising multiple thin films of one quarter wavelength stacks of alternating high and low dielectric materials have been available for many years and are characterized as being highly flexible optical components permitting precision design location of filter wavelengths with maximum inband transmission. These interference filters are normally deposited onto glass or other transmitting stable materials which can retain their structure during evaporation or sputtering of the films onto the substrate at elevated temperatures. They are designed to reflect specific wavelengths or spectral bands and are therefore useful for protecting the eye or viewer against lasers. However, because the thin film thickness is designed to bear a one quarter wavelength (or other factor) relationship to the wavelength of interest, the filter will respond differently to laser rays entering the filter at off normal incidence. As the path lengths through the layers of dielectric materials increase due to a greater angle of incidence, there is a shift of the filter response to shorter wavelengths. Since the interference filters of interest are designed to reflect incident laser radiation at specific wavelengths, the laser blocking wavelength would then be shifted to a wavelength where it would not be useful in providing protection. Thus, the interference filter because of its deposition at high temperatures and its change of response at off axis incidence provides some problems for use as a laser shield. In addition, these are delicate filters and would provide no ballistic protection from flying objects to the viewer. The high energy levels employed in lasers as well as the nature of the systems in which they are incorporated makes it advisable to provide ballistic protection in laser shield.